I attended a CASA human factors course in Adelaide about 4 years ago and the subject of fatigue effects on engineers was thoroughly discussed. We were presented with some pretty scary figures on the maintenance error rate escalation in comparison to hours of duty. We were pretty much told we had a duty of care to ensure fatigue was managed.
When we asked CASA why, if it is such a glaring safety issue, they would not take steps to regulate engineer duty times as they do for pilots, SILENCE.
Off the record I was informed that there wasnt a lobby strong enough for it, given that the Majors ( Q et al ) would fight tooth and nail against it.